The present invention relates to a method for folding an airbag that is attached, for example, to a side of a vehicle seat, an airbag folded in such a manner, and to an airbag apparatus that is equipped with the airbag.
The airbag of an airbag apparatus of this type is incorporated in a side of the backrest of a seat in a folded state. When an impact that is equal to or greater than a predetermined level is applied to the vehicle, the airbag is inflated and deployed between a sidewall of the vehicle body and the seat. The inflated and deployed airbag separates the lumbar region, the abdomen, and a shoulder of an occupant from the sidewall of the vehicle body, and absorbs impact applied to the vehicle body.
In such an airbag apparatus, the airbag is incorporated in the backrest of the seat in a folded state. For example, Japanese Laid-Open Patent Publication No. 9-272393 discloses an invention related to a method for folding an airbag having expansion portions.
In the airbag apparatus disclosed in the publication, an airbag 101 has a central expansion portion 102, an upper expansion portion 103, and a lower expansion portion 104 as shown in FIG. 13(a). The upper expansion portion 103 is inflated upward above the central expansion portion 102, and the lower expansion portion 104 is inflated downward below the central expansion portion 102. Then, as shown in FIG. 13(b), the airbag 101 is folded with the upper expansion portion 103 and the lower expansion portion 104 tucked in the central expansion portion 102 from above and below. That is, the upper expansion portion 103 and the lower expansion portion 104 are tucked in the central expansion portion 102 while being brought closer to each other. Subsequently, as shown in FIG. 13(c), the airbag 101 is folded to form a bellows-like portion toward a proximal end 105.
When expansion gas is supplied to the interior of the airbag 101 folded in the above described manner, the portion folded in a bellows is unfolded along a deploying direction indicated by arrow A in FIG. 13(c). Since the upper expansion portion 103 and the lower expansion portion 104 are each folded at a folding line 107 that extends from the proximal end 105 to a distal end 106 and is parallel to the deploying direction, the upper expansion portion 103 and the lower expansion portion 104 are inflated upward and downward substantially simultaneously when the bellows-like portion is unfolded.
In the method for folding airbag according to the prior art, the lower expansion portion 104 and the upper expansion portion 103 are each tucked into the central expansion portion 102 by folding the airbag at the folding lines 107, which extend along the deploying direction of the airbag 101. Therefore, the size of a portion of the airbag 101 that can be tucked inward is limited if a joint section, where facing portions of the airbag are fastened to each other, is formed in the lower or upper expansion portions 104, 103, or if a narrow section, where the thickness of the airbag when inflated is less than the other portions, is formed,. In such a case, the packaged size of the airbag after being folded cannot be more compact beyond a certain limit.